This invention relates to apparatus for monitoring repeatedly the absorption of electromagnetic radiation by a plurality of specimens occurring during a period of time. More particularly, this invention concerns an apparatus by which each of a plurality of samples provides a plurality of aliquots which can be subjected to chemical reaction with different reagents. The absorbance of each aliquot repeatedly is measured during a predetermined reaction time. The inputting of the samples, obtaining their aliquots, selecting and adding of reagents, and the absorbance measuring all can be effected in a continuous mode as well as a stat and a batch mode of operation. The term "aliquot" as employed herein is a noun meaning a portion of a sample.
Apparatus described hereinafter would be well suited for the measurement of kinetic reactions such as useful in enzyme analysis as well as end point measurement. Many chemical reactions require from a few seconds to many minutes to be completed and, during such kinetic reaction time, it is often important to observe the progress of the reaction by making measurements several times. One form of measurement is ascertaining the absorbance of electromagnetic radiation of a particular wavelength by the analyte. Typically, enzyme reaction measurements have been accomplished by batch handling methods and apparatuses requiring a considerable amount of preparation and manipulation by the laboratory technician. The nature of the process cannot help but result in relatively low throughput. Examples of batch operating enzyme analyzers are disclosed in Wood et al U.S. Pat. No. 3,344,702 and Liston U.S. Pat. No. 3,748,044, the latter having automated the aliquot preparation and reagent dispensing, but being limited to a single chemistry determination for all of the aliquots in the batch being processed.
In contrast to the batch mode a more efficient method is the continuous mode in which the apparatus can remain operating as long as there are samples to be tested, with old samples and their tested aliquots being "replaced" by new samples and their aliquots without interruption of the operation of the testing apparatus. Such continuous operation is well known in biological chemistry testing systems and is taught, for example, in Jones U.S. Pat. No. 3,799,744 and Hoskins et al U.S. Pat. No. 3,883,305, in which separate chemistry tests can be made for several different aliquots from the same sample.
A disadvantage of such systems is that they are capable of making only a single photometric measurement on a given aliquot and even if an attempt is made to achieve measurement of kinetic reaction by, for example two time-separated measurements, these must be effected on different aliquots of the same sample. Thus, these systems are not designed to measure kinetic reactions by multiple point observations on a single aliquot.
Recently published Greaves et al U.S. Pat. No. 3,966,322 discloses a specimen investigating apparatus suitable for measuring kinetic reactions in a continuous operations mode. Greaves et al teaches that illumination of the plurality of specimens, which are circumferentially mounted in cuvettes around the periphery of a turntable, originates from a single non-rotating light source that projects a beam of light vertically down the axis of the hollow shaft of the turntable. Optical elements then divert and direct the light beam radially outward toward one of the specimen holding cuvettes and to a radially inwardly reflected or directed return path that terminates with a vertically down-the-axis output to a fixed light detector. The optical elements providing this tortuous path for the light beam are mounted for rotation around the same axis but at a higher speed than the specimen turntable. With only one light source and one optical train, only one specimen can be monitored at any one instant and each specimen is monitored only once per revolution of the optical train.
Greaves et al as well as another apparatus which has been described recently that is similar to Greaves et al has two disadvantages. The light source for this type of device comprises a tungsten or similar lamp having a filament. The light source remains fixed while the optical elements of the train rotate. The orientation of the lamp filament with respect to the optical elements of the train will change with rotation, exacerbated by precession and the intersection of the light beam with the photodetector at the end of the long optical path will change similarly. The obvious sources of error then become the following:
(1) The light input varies because light emitted from different parts of the lamp filament is non-uniform and the optical elements of the train look at different parts of the filament at different times.
(2) The output from the photodetector varies because it has different response in different areas of its sensitive surface and the incident energy beam impinges varying areas of this surface at different times.
Another prior art device is disclosed in DeMendez et al U.S. Pat. No. 3,829,221 in which a single light source and photoresponsive detector rotate in unison. The cuvettes are necessarily stationary. This enables only batch methods of measurement of absorbance using a single wavelength.